Method for assembling gas sensor, and gas sensor assembly apparatus

ABSTRACT

A method for assembling a gas sensor includes fitting through holes of annular mounting parts with an element dummy disposed vertically and whose cross-sectional shape perpendicular is similar to that of a sensor element. The annular mounting parts are a plurality of parts including a ceramic powder compact. A tubular body is fitted with outer peripheries of the annular mounting parts, and then, the element is abuttingly disposed on an upper end of the dummy. Subsequently, the dummy is moved vertically downward to fit the through holes of the annular mounting parts with the element, thereby obtaining a workpiece. The workpiece is vertically inverted, and with the element tip being in contact with a sealing assist jig that has a buffer performance, the upper end of the uppermost annular mounting part is pressed vertically downward to compress the powder compact, thereby sealing an inside of the tubular body.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a method for assembling a gas sensorincluding a ceramic sensor element and to an assembly apparatus for usein assembling the same.

2. Description of the Background Art

A gas sensor including a sensor element formed of oxygen-ion conductivesolid electrolyte ceramic such as zirconia (ZrO₂) has beenconventionally known as a device that measures the concentration of apredetermined gas component of a measurement gas such as an exhaust gasand a combustion gas in an internal combustion engine, usually a carengine.

In such a gas sensor, an elongated-plate-shaped ceramic sensor element(detection element) is usually fixed by a plurality of ceramicsupporters which are ceramic insulators glass and by ceramic powdercompacts each filled between the ceramic supporters, such as talc, andis hermetically sealed with the powder compacts in a metal housing and ahollow portion of a cylindrical inner tube welded and fixed to thehousing. The method and apparatus for preferably assembling such a gassensor have been known (for example, see WO 2013/005491 and JapanesePatent Application Laid-Open No. 2005-37372).

In the technique disclosed in WO 2013/005491, even when a sensor elementwarps and a dimensional tolerance between the sensor element and aplurality of members (annular mount members, annular mounting parts) tobe annularly mounted is small, the annular mount members (annularmounting parts) can be annularly mounted with reliability.

In the technique disclosed in WO 2013/005491, the annular mount membersare annularly mounted to the sensor element from an end at the side atwhich the opening for introducing a measurement gas into the element isprovided. Thus, the application of this technique to a sensor element,whose surface at the side of the relevant end is covered with aprotective film (protective layer), is not preferred because theprotective film may be damaged or peeled off.

Japanese Patent Application Laid-Open No. 2005-37372 discloses a methodfor manufacturing a gas sensor including a detection element whose oneend side is covered with a protective layer. In the method disclosed inJapanese Patent Application Laid-Open No. 2005-37372, however, aplurality of annular mounting parts are once annularly mounted to a pinmember similar in shape to the detection element, the pin member ispulled out so that the plurality of annular mounting parts are stacked,and then the detection element is inserted into the stacked annularmounting parts. Consequently, the annular mounting parts are likely toslide out of place when the pin member is pulled out or the detectionelement is inserted.

SUMMARY OF THE INVENTION

The present invention is directed to a method for assembling a gassensor including a ceramic sensor element and an assembly apparatus foruse in assembling the same.

A method for assembling a gas sensor according to the present inventionincludes the steps of: (a) disposing an element dummy with itslongitudinal direction coinciding a vertical direction, the elementdummy having a shape similar to a shape of a sensor element includingceramic as a main constituent material and having an elongated shape;(b) fitting through holes of annular mounting parts with the elementdummy from vertically above, the annular mounting parts each having adisc shape or cylindrical shape, the through holes each having a shapecorresponding to a cross-sectional shape of the sensor element; (c)fitting a tubular body with outer peripheries of the annular mountingparts from vertically above; (d) abuttingly disposing the sensor elementon an upper end of the element dummy such that the element dummy and thesensor element are arranged in line with each other; (e) moving theelement dummy vertically downward to move down the sensor element andfitting the through holes of the annular mounting parts with the sensorelement, to thereby obtain a workpiece including the sensor element, theannular mounting parts, and the tubular body; (f) vertically inverting aposture of the workpiece; and (g) pressing the annular mounting parts.In the step (a), a plurality of types of parts including a powdercompact of ceramic are fitted with the element dummy as the annularmounting parts. The step (g) includes a step of compressing the powdercompact and is performed at least after the step (f).

According to the present invention, the annular mounting parts arealways annularly mounted to the element dummy or the sensor element inthe assembly of the gas sensor, thus preferably preventing an occurrenceof a problem in which the sensor element cannot be assembled due to anoccurrence of a positional deviation. Additionally, breakage of theelement tip is preferably prevented when the inside of the gas sensor issealed with a powder compact.

Preferably, in the step (g), with the tip of the sensor element, whichis located as a lowermost end of the workpiece after the step (f), beingin contact with the sealing assist jig, the part located at an uppermostposition among the annular mounting parts is pressed verticallydownward, so that the powder compact is compressed to seal the inside ofthe tubular body. The sealing assist jig has a buffer performanceagainst an impact exerted from vertically above.

In another aspect of the present invention, the step (g) includes (g-1)a step of compressing the powder compact of the workpiece being in afirst posture, and (g-2) a step of compressing the powder compact of theworkpiece being in a second posture. The first posture is a posture ofthe workpiece before being vertically inverted in the step (f). Thesecond posture is a posture of the workpiece after being verticallyinverted in the step (f). Letting an upper end and a lower end of thesensor element when the workpiece is in the first posture berespectively a first tip and a second tip: in the step (g-1), while thesensor element is positioned from below the second tip with apredetermined positioning jig, a first force is applied to the annularmounting parts vertically upward to compress the powder compact; in thestep (f), the workpiece in which the powder compact has been compressedin the step (g-1) is vertically inverted; and in the step (g-2), whilethe workpiece vertically inverted in the step (f) is supported frombelow and simultaneously the first tip of the sensor element located ata lowermost end of the workpiece is prevented from abutting anothermember, a second force greater than the first force is applied to theannular mounting parts vertically downward to further compress thepowder compact, to thereby seal an inside of the tubular body.

According to the aspect, a gas sensor is assembled with a low risk ofchipping or cracking occurring in the sensor element compared with amanner of performing sealing only once.

The present invention therefore has an object to provide a method forassembling a gas sensor capable of preferably assembling a gas sensor.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an external perspective view of a gas sensor (morespecifically, a main body thereof) to be assembled in embodiments;

FIG. 2 is a partial cross-sectional view of main components inside thegas sensor 1;

FIG. 3 schematically shows how a washer 7, ceramic supporters 8, andpowder compacts 9 are annularly mounted to a sensor element 10;

FIG. 4 is a block diagram showing a schematic configuration of anassembly apparatus 100;

FIGS. 5A, 5B, and 5C are schematic cross-sectional views of an assembly40 according to a first embodiment during assembly;

FIGS. 6A, 6B, and 6C are schematic cross-sectional views of the assembly40 according to the first embodiment during assembly;

FIG. 7 is a schematic cross-sectional view of the assembly 40 accordingto the first embodiment during assembly;

FIGS. 8A and 8B are schematic cross-sectional views of the assembly 40according to the first embodiment during assembly;

FIGS. 9A and 9B are schematic cross-sectional views of the assembly 40according to the first embodiment during assembly;

FIG. 10 is a schematic cross-sectional view of a modification of thefirst embodiment;

FIG. 11 is a block diagram showing a schematic configuration of anassembly apparatus 1100;

FIGS. 12A and 12B are schematic cross-sectional views of an assembly 40according to a second embodiment during assembly;

FIG. 13 is a schematic cross-sectional view of the assembly 40 accordingto the second embodiment during assembly;

FIGS. 14A and 14B are schematic cross-sectional views of the assembly 40according to the second embodiment during assembly; and

FIGS. 15A and 15B are schematic cross-sectional views of the assembly 40according to the second embodiment during assembly.

DESCRIPTION OF THE PREFERRED EMBODIMENTS First Embodiment Configurationof Gas Sensor

FIG. 1 is an external perspective view of a gas sensor (morespecifically, a main body thereof) 1 to be assembled in a firstembodiment. FIG. 2 is a partial cross-sectional view of main componentsinside the gas sensor 1. In this embodiment, the gas sensor 1 serves todetect a predetermined gas component (e.g., NOx) by a sensor element 10(FIG. 2) inside the gas sensor 1.

The sensor element 10 is an elongated columnar or thin-plate-shapedmember including, as a main constituent material, an element body ofoxygen-ion conductive solid electrolyte ceramic such as zirconia. Thesensor element 10 has a configuration in which a gas inlet, an internalspace, and the like are provided at a side of a first tip 10 a, andvarious electrodes and a wiring pattern are provided on the surface andinside of the element body. In the sensor element 10, a detection gasintroduced into the internal space is reduced or decomposed in theinternal space, to thereby generate oxygen ions. The gas sensor 1determines the concentration of the gas component based on a fact thatan amount of oxygen ions flowing through the element is proportional tothe concentration of the gas component in a detection gas. Withreference to FIG. 2, the surface coinciding the front is referred to asa main surface S1 of the sensor element 10, and the surface that isperpendicular to the main surface S1 and extends longitudinally isreferred to as a lateral surface S2. The surface of the sensor element10 within a predetermined range from the first tip 10 a in thelongitudinal direction of the sensor element 10 is covered with aprotective film P (see FIG. 2). The protective film P is a porous filmprovided to protect the first tip 10 a and its vicinity from thermalshock, which is made of, for example, Al₂O₃ and has a thickness ofapproximately 10 to 2000 μm, and is also referred to as athermal-shock-resistant protective film. In light of its objective, theprotective film P should preferably be formed so as to resist forces upto approximately 50 N. The formation range of the protective film P inFIG. 2 and the following drawings is merely an example, and actually,the formation range is appropriately determined in accordance with aspecific structure of the sensor element 10.

The exterior of the gas sensor 1 is mainly composed of a first cover 2,a fixing bolt 3, and a second cover 4.

The first cover 2 is an approximately cylindrical exterior member thatprotects a portion of the sensor element 10 which directly comes intocontact with the detection gas at the time of use, which is specificallythe first tip 10 a including a gas inlet 11 and closed spaces 12 (bufferspace 12 a, first internal space 12 b, second internal space 12 c). Foreasy understanding, FIG. 2 and the following drawings show that the gasinlet 11 and the closed spaces 12 (buffer space 12 a, first internalspace 12 b, second internal space 12 c) are formed on the main surfaceS. In actuality, however, these parts are not exposed on the mainsurface S1 but are each provided inside the sensor element 10 except forthe gas inlet 11 being open at the first tip 10 a that is the lowermostend of the sensor element 10 in FIG. 2.

More specifically, the first cover 2 has a double-layer structure of anoutside cover 2 a and an inside cover (not shown). Each of the outsidecover 2 a and the inside cover has a cylindrical shape and is closed atone side, and has a plurality of through holes in its lateral portion,through which a gas passes. FIG. 1 illustrates through holes H1 providedin the outside cover 2 a, which are merely an example. The position andthe number of through holes disposed can be appropriately determined inconsideration of how a measurement gas flows into the first cover 2.

The fixing bolt 3 is an annular member to be used when the gas sensor 1is fixed at a measurement position. The fixing bolt 3 includes athreaded bolt portion 3 a and a holding portion 3 b to be held when thebolt portion 3 a is screwed. The bolt portion 3 a is screwed with a nutprovided at a position at which the gas sensor 1 is mounted. Forexample, the bolt portion 3 a is screwed with a nut portion provided inthe car exhaust pipe, which causes the gas sensor 1 to be fixed to theexhaust pipe in such a manner that the first cover 2 side of the gassensor 1 is exposed in the exhaust pipe.

The second cover 4 is a cylindrical member that protects other parts ofthe gas sensor 1. From the end of the second cover 4, a cable C forelectrically connecting the gas sensor 1 and a drive control part (notshown) extends.

FIG. 2 shows the internal configuration of the gas sensor 1, morespecifically, the configuration of the gas sensor 1 except for the firstcover 2, the fixing bolt 3, and the second cover 4 shown in FIG. 1.

As shown in FIG. 2, inside the gas sensor 1, a washer 7, three ceramicsupporters 8 (8 a, 8 b, 8 c), and two powder compacts 9 (9 a, 9 b) areeach annularly mounted to the portion of the sensor element 10 exceptfor the first tip 10 a, which includes the gas inlet 11 and the like,and a second tip 10 b, which includes terminals 13 for connection withthe cable C, in such a manner that the sensor element 10 is positionedabout their axes. The ceramic supporters 8 are made of ceramicinsulator. The powder compacts 9 are obtained by shaping ceramic powderssuch as talc. In the following description, the washer 7, the ceramicsupporters 8, and the powder compacts 9 may be collectively referred toas annular mounting parts.

FIG. 3 schematically shows how the washer 7, the ceramic supporters 8 (8a, 8 b, 8 c), and the powder compacts 9 (9 a, 9 b) are annularly mountedto the sensor element 10.

As shown in FIG. 3, such annular mounting is enabled by inserting theend (second tip 10 b) of the sensor element 10 at the side, at which theprotective film P is not provided, into the ceramic supporter 8 c, thepowder compact 9 b, the ceramic supporter 8 b, the powder compact 9 a,the ceramic supporter 8 a, and the washer 7 in the stated order. Therespective members have a circular plate shape or cylindrical shape. Forsuch annular mounting, a through hole 7 h of cylindrical shape isprovided at the center axis of the washer 7, and through holes 8 ah, 9ah, 8 bh, 9 bh, and 8 ch of rectangular shape corresponding to thecross-sectional shape of the sensor element 10 are respectively providedin the ceramic supporter 8 a, the powder compact 9 a, the ceramicsupporter 8 b, the powder compact 9 b, and the ceramic supporter 8 c.These through holes are fitted with the sensor element 10, therebycausing the respective members to be annularly mounted to the sensorelement 10. The portion of the ceramic supporter 8 c opposite thethrough hole 8 ch is an opening 8 ch′ larger than the through hole 8 ch.The washer 7, the ceramic supporters 8, and the powder compacts 9 aredisposed coaxially with one another.

From the viewpoint of attaining airtightness, the through holes of theceramic supporters 8 and the through holes of the powder compacts 9 areconfigured such that a difference with the design cross-sectional sizeof the sensor element 10 is 0.25 to 0.35 mm and a dimensional toleranceis 0.1 mm. The through hole 7 h of the washer 7 is provided such that adifference with the design cross-sectional size of the sensor element 10is at least 1 mm or more and 1.3 mm or less. The washer 7, the ceramicsupporters 8, and the powder compacts 9 are configured so as to have adifference of no more than approximately 0.35 mm in outside diametervalue.

As shown in FIG. 2, a cylindrical tubular body (inner tube weldedproduct) 30 including a housing 5 being a ceramic cylindrical member andan inner tube 6 being a metal cylindrical member, which are integratedwith each other, is annularly mounted to the outer peripheries of thewasher 7, the ceramic supporters 8 (8 a, 8 b, 8 c), and the powdercompacts 9 (9 a, 9 b). In the following description, the body having theconfiguration in which the tubular body 30 is annularly mounted isreferred to as an assembly 40.

The tubular body 30 is formed integrally by welding a bend 6 a bentoutwardly, which is included at one end of the inner tube 6, to an endsurface 5 s of the housing 5. The housing 5 and the inner tube 6 havesubstantially the same inside diameter and are connected coaxially. Theinside diameter of the tubular body 30 is set to be greater than adesign value of the maximum outside diameter of each annular mountingpart.

At one side inside the housing 5, a tapered portion 5 c is provided. Atthe position of the inner tube 6 immediately above the washer 7, arecess 6 b recessed inwardly is formed. The tapered portion 5 c and therecess 6 b cause the washer 7, the ceramic supporters 8 (8 a, 8 b, 8 c),and the powder compacts 9 (9 a, 9 b) that are annularly mounted to thesensor element 10 to be locked inside the tubular body 30.

More specifically, the powder compacts 9 are compressed after beingannularly mounted, and are accordingly in intimate contact with thesensor element 10. The recess 6 b is provided after the powder compacts9 are compressed. With the intimate contact achieved between the powdercompacts 9 and the sensor element 10, the sensor element 10 is fixedinside the tubular body 30, and a space between the first tip 10 a sideof the sensor element 10, which includes the gas inlet 11, and thesecond tip 10 b, which includes the terminals 13 for connection with thecable C, is sealed. This achieves airtightness between a measurement gasspace, which is in contact with the first tip 10 a of the sensor element10 and in which a detection gas (measurement gas) is present, and areference gas space, which is in contact with the second tip 10 b and inwhich a reference gas such as air is present. The recess 6 b is providedto keep the compressed states of the powder compacts 9.

The resultant product obtained by coating the assembly product 40 havingthe above configuration with the first cover 2, the fixing bolt 3, andthe second cover 4 is the gas sensor 1. Specifically, the first cover 2is connected to a tubular portion 5 a at the tip of the housing 5. Thefixing bolt 3 is annularly mounted to the outer periphery of the housing5 so as to come into contact with a projection portion (flanged portion)5 b. Moreover, the second cover 4 is mounted so as to be fitted into anannular groove between the fixing bolt 3 and the housing 5, which isformed by the annular mounting above.

The above-mentioned configuration allows the gas sensor 1 to completelycut off the atmosphere (the atmosphere in the first cover 2) around thefirst tip 10 a of the sensor element 10 from the outside atmospherewhile being mounted at a predetermined position. This enables accuratemeasurement of the concentration of a target gas component in adetection gas.

Procedure for Assembling Assembly

The procedure for assembling the assembly 40 performed in thisembodiment will now be described. FIG. 4 is a block diagram showing aschematic configuration of the assembly apparatus 100 that performs theassembly above.

The assembly apparatus 100 includes a control part 101, an operationpart 102, a display part 103, and a storage part 104. The control part101 is mainly composed of a CPU 101 a, a ROM 101 b, and a RAM 101 c andcontrols the overall operation of the assembly apparatus 100. Theoperation part 102 is an input interface composed of switches, buttons,a touch panel, and the like for providing various execution instructionsto the assembly apparatus 100. The display part 103 includes a displayfor displaying various operation menus and the operation state of theassembly apparatus 100 and instruments. The storage part 104 mainlystores an operation program 104 p and operational condition data (notshown) of the assembly apparatus 100. The assembly apparatus 100automatically processes a series of assembly operations described belowby the control part 101 executing the operation program 104 p.

The assembly apparatus 100 further includes, as components that actuallyexecute the assembly operations, a dummy elevating mechanism 120performing an operation of moving up and down the element dummy 121, anannular mounting parts transport mechanism 130 transporting annularmounting parts from an annular mounting parts wait part 131 to apredetermined position, a housing fixing jig drive mechanism 140performing an operation of movement a housing fixing jig 141, an elementtransport mechanism 150 transporting a sensor element 10 from an elementwait part 151 to a predetermined position, an element guide jig drivemechanism 160 performing an operation of movement an element guide jig161, an inversion mechanism 170 performing an operation of inverting aworkpiece 40β (described below) with an inversion jig 171, a sealing jigelevating mechanism 180 performing an operation of moving up and down asealing jig 181, a crimp jig drive mechanism 190 performing an operationof movement a crimp jig 191, and an assembly transport mechanism 200transporting a complete assembly 40 to an assembly wait part 201.

FIGS. 5A, 5B, 5C, 6A, 6B, 6C, 7, 8A, 8B, 9A, and 9B are schematiccross-sectional views of the assembly 40 during assembly for explainingthe procedure in assembling the assembly 40 by the assembly apparatus100. In FIGS. 5A to 9B, the vertically upward direction is representedby the z-axis direction.

As shown in FIG. 5A, first, the element dummy 121 is inserted through asupport 110.

The support 110 is a member for supporting the annular mounting partsfrom below in the step of assembling the assembly 40. The support 110has a flat horizontal surface 110 s at the vertical upper side and has athrough hole 110 h through which the element dummy 121 is inserted.

The element dummy 121 is a member whose cross-section perpendicular toits longitudinal direction has a shape similar to the longitudinalcross-sectional shape of the sensor element 10 and which has anelongated plate shape similarly to the sensor element 10. The elementdummy 121 is movable up and down vertically by the dummy elevatingmechanism 120 not shown in FIGS. 5A, 5B, and 5C. The element dummy 121,however, does not need to be made of ceramic similarly to the sensorelement 10 and may be formed of an appropriate material in considerationof durability, wear resistance, or the like. The element dummy 121 has athickness and a width somewhat greater than those of the sensor element10 though it is smaller than the through holes of the ceramic supporters8 and the powder compacts 9. The element dummy 121 is inserted into thesupport 110 from the vertical lower side of the support 110 by the dummyelevating mechanism 120 and is disposed with its longitudinal directioncoinciding the vertical direction. In this case, the dummy elevatingmechanism 120 functions as dummy disposing means for disposing theelement dummy 121 with its longitudinal direction coinciding thevertical direction. In such a case, the element dummy 121 is inserted upto a position at which the distance between the vertical upper portionof the element dummy 121 and the horizontal surface 110 s of the support110 is greater than a total of the thicknesses of all the annularmounting parts.

After the insertion of the element dummy 121 completes, subsequently,the annular mounting parts are annularly mounted to the element dummy121, and then, the tubular body 30 is annularly mounted.

First, the annular mounting parts transport mechanism 130 not shown inFIGS. 5A, 5B, and 5C transports the annular mounting parts, which havebeen transported from the outside of the apparatus in advance and causedto wait at the annular mounting parts wait part 131, to the elementdummy 121 in the order of the washer 7, the ceramic supporter 8 a, thepowder compact 9 a, the ceramic supporter 8 b, the powder compact 9 b,and the ceramic supporter 8 c, and fits the through holes of therespective parts with the element dummy 121. This results in a state inwhich, as shown in FIG. 5B, the respective annular mounting partssequentially fitted with the element dummy 121 are supported by theupper end of the support 110 from vertically below. In this case, theannular mounting parts transport mechanism 130 functions as annularmounting part fitting means for fitting the through holes of the annularmounting parts with the element dummy 121.

When the annular mounting completes, subsequently, the annular mountingparts transport mechanism 130 transports the tubular body 30, which hasbeen transported from the outside of the apparatus and caused to wait atthe annular mounting parts wait part 131 as described above, to abovethe element dummy 121 with the annular mounting parts annularly mountedthereto, and further, moves down the tubular body 30 with the inner tube6 pointing vertically downward to fit the tubular body 30 with the outerperipheries of the annular mounting parts. This results in a state inwhich, as shown in FIG. 5C, the annular mounting parts fitted with thetubular body 30 are supported by the upper end of the support 110 fromvertically below. In this case, the annular mounting parts transportmechanism 130 functions as tubular body fitting means for fitting thetubular body 30 with the outer peripheries of the annular mountingparts.

More specifically, the annular mounting parts transport mechanism 130moves down the tubular body 30 until a projection portion 5 b of thehousing 5 abuts a support part 141 a that constitutes the housing fixingjig 141 from above. This abutment allows the tubular body 30 to besupported by the support part 141 a from vertically below. In otherwords, the vertical height level of the tubular body 30 is defined bythe support part 141 a. After the projection portion 5 b is supported bythe support part 141 a from vertically below in the above state, thehousing fixing jig drive mechanism 140 not shown in FIG. 5 moves down amovable part 141 b of the housing fixing jig 141, which has retracted toa predetermined retraction position (not shown), toward the projectionportion 5 b from vertically above as indicated by the arrow AR1 andcauses the movable part 141 b to abut the projection portion 5 b. Asshown in FIG. 5C, consequently, the housing fixing jig 141 grips andfixes the projection portion 5 b of the housing 5. In other words, thetubular body 30 including the housing 5 is fixed by the housing fixingjig 141.

The transport of the washer 7, the ceramic supporters 8, and the powdercompacts 9, fitting of these annular mounting parts with the elementdummy 121, and fitting of the tubular body 30 with the outer peripheriesof these annular mounting parts by the annular mounting parts transportmechanism 130 may be performed by an annular mounting parts transportmechanism 130 including transport arms whose constructions and materialscorrespond to the shapes and materials of the respective parts, usingthese transport arms.

The support part 141 a and the movable part 141 b constituting thehousing fixing jig 141 may have any shape in which the projectionportion 5 b of the housing 5 can be gripped and fixed from verticallyabove. For example, the support part 141 a and the movable part 141 bmay be formed of a pair of members of symmetrical shape or may be formedof one member of C-shape or U-shape in plan view. The support part 141 aand the movable part 141 b may have different shapes.

When the tubular body 30 including the housing 5 is fixed as describedabove, subsequently, as shown in FIG. 6A, the sensor element 10 isabuttingly disposed to the element dummy 121 so as to be arranged inline with the element dummy 121, with the sensor element 10 being in aposture in which its tip (first tip 10 a) at the side at which theprotective film P is formed is located at the upper side. This positionof the sensor element 10 is implemented by the movement of the elementtransport mechanism 150 not shown in FIGS. 6A, 6B, and 6C oftransporting the sensor element 10, which has been transported from theoutside of the apparatus in advance and caused to wait at the elementwait part 151, to above the element dummy 121 so as not to come intocontact with the protective film P and further of moving down the sensorelement 10 vertically above the element dummy 121 and causing the sensorelement 10 to abut the upper end of the element dummy 121, as indicatedby the arrow AR2 in FIG. 6A. The element transport mechanism 150 holdsthe sensor element 10 at this position. In this case, the elementtransport mechanism 150 functions as element disposing means forabuttingly disposing the sensor element 10 on the upper end of theelement dummy 121. In FIGS. 6A, 6B, and 6C and the following drawings,the thickness of the protective film P is exaggerated. The thickness ofthe protective film P is actually designed to such an extent that doesnot affect the annular mounting of the annular mounting parts and thetubular body 30 described below.

A specific configuration of the element transport mechanism 150 may beany configuration in which the sensor element 10 can be preferablytransported and held so as not to come into contact with the protectivefilm P.

When the sensor element 10 is disposed as described above, the elementguide jig drive mechanism 160 not shown in FIGS. 6A, 6B, and 6C runs, sothat the element guide jig 161 is disposed at the position lateral tothe sensor element 10, as indicated by the arrow AR3 in FIG. 6A. Theelement guide jig 161 is disposed to support and guide the sensorelement 10 when the sensor element 10 is moved vertically downward. Thesurface of the element guide jig 161, which faces the sensor element 10,is thus formed of a material that does not damage the sensor element 10if the sensor element 10 comes into contact with the surface, and isdisposed so as to extend vertically at a position at which the surfacecomes closer to or comes into contact with the sensor element 10.

When the element guide jig 161 is disposed, holding of the sensorelement 10 by the element transport mechanism 150 is released, so thatthe sensor element 10 enters the state in which the lower end (secondtip 10 b) thereof is supported by the element dummy 121. In addition,the dummy elevating mechanism 120 not shown in FIGS. 6A, 6B, and 6C runsagain, so that as indicated by the arrow AR4 in FIG. 6B, the elementdummy 121 is moved vertically downward. Correspondingly to the elementdummy 121 moving downward, the sensor element 10 whose lower end (secondtip 10 b) has been supported by the element dummy 121 also movesvertically downward. In the through holes of the annular mounting parts,accordingly, the sensor element 10 gradually replaces the element dummy121, resulting in a state in which the annular mounting parts areannularly mounted to the sensor element 10. In this case, the dummyelevating mechanism 121 functions as element fitting means for fittingthe through holes of the annular mounting parts with the sensor element10.

The annular mounting parts are always annularly mounted to the elementdummy 121 or the sensor element 10 in the manner above, which preferablyrestricts an occurrence of a problem in which annular mounting partshave a positional deviation and the sensor element 10 accordingly cannotbe incorporated.

As the sensor element 10 moves downward to some extent so that thesensor element 10 begins to move vertically downward without beingsupported and guided by the element guide jig 161, the element guide jigdrive mechanism 160 runs again to separate the element guide jig 161from the sensor element 10, as indicated by the arrow AR6 in FIG. 6B.This is also for preventing the protective film P from coming intocontact with the element guide jig 161.

The sensor element 10 is moved down by moving down the element dummy 121until, as shown in FIG. 6C, the sensor element 10 penetrates through thewasher 7 and the upper end (first tip 10 a) of the sensor element 10reaches the position of the upper end of the housing 5. Although aspecific degree to which the upper end of the sensor element 10 projectsfrom the housing 5 can be appropriately determined, as described below,the sensor element 10 is positioned at a predetermined position beforethe assembly 40 is eventually obtained.

After the completion of the sensor element 10 moving downward, theinversion mechanism 170 not shown in FIG. 7 vertically inverts theposture of the assembly 40 during assembly which has undergone up to theinsertion of the sensor element 10 (which is hereinafter referred to asa workpiece 40β).

Specifically, first, the inversion mechanism 170 drives the inversionjig 171 simultaneously with the release of the fixing by the housingfixing jig 141 (retraction of the housing fixing jig 141), and as shownin FIG. 7, the inversion jig 171 is caused to hold the workpiece 40βfrom the lateral side of the workpiece 40β. More specifically, theworkpiece 40β is held from the lateral side of the housing 5.

Subsequently, as indicated by the arrow AR7, the inversion mechanism 170rotates the inversion jig 171 holding the workpiece 40β by 180° togetherwith the workpiece 40β. This vertically inverts the posture of theworkpiece 40β. In this case, the inversion jig 171 and the inversionmechanism 170 function as inversion means for vertically inverting theposture of the workpiece 40β. Specific configurations of the inversionjig 171 and the inversion mechanism 170 may be any configuration inwhich the posture of the workpiece 40β can be inverted preferably.

Further, subsequent to the inversion of its posture, the inversionmechanism 170 moves the inversion jig 171 while holding the workpiece40β, thereby disposing the workpiece 40β such that the first tip 10 a ofthe sensor element 10 covered with the protective film P, which ispositioned as the lowermost end after the inversion, comes into contactwith the vertical upper end of a sealing assist jig 111.

The sealing assist jig 111 is a member for positioning the sensorelement 10 (restricting a positional deviation of the sensor element 10)in sealing by compression of the powder compacts 9 (9 a, 9 b). Thesealing assist jig 111 includes an impact buffer 112 formed of amaterial (cushion material) having a buffer performance (anti impactperformance) against an impact (load) exerted from above, on thevertical upper end. Specifically, the impact buffer 112 is provided soas to deform (contract) vertically in accordance with the magnitude ofthe impact (load) to be exerted, as indicated by the arrow AR8 in FIG.7, thereby mitigating the impact (load) exerted. The workpiece 40β whoseposture has been inverted as described above is disposed in such amanner that the first tip 10 a of the sensor element 10, which iscovered with the protective film P, is in contact with the impact buffer112.

The impact buffer 112 is formed of a material having Rockwell hardness(HRC) of 1 or more and 200 or less to have a thickness of approximately0.1 mm or more and 1.0 mm or less in the vertical direction. Bysatisfying these values, the assembly apparatus 100 preferably mitigatesimpacts exerted on the protective film P and the sensor element 10 andpreferably restricts the displacement of the sensor element 10 insealing by the sealing jig 181 described below. As the material for theimpact buffer 112, a resin material such as polypropylene isexemplified. The impact buffer 112 may be provided densely or may beprovided as a porous body such as foam.

When the posture of the workpiece 40β is inverted and is disposed on thesealing assist jig 111 in the manner described above, subsequently, asshown in FIGS. 8A and 8B, the inside of the workpiece 40β is sealed bythe compression of the powder compacts 9 (9 a, 9 b) using the sealingjig 181.

The sealing jig 181 is a cylindrical member with its longitudinaldirection coinciding the vertical direction. The sealing jig 181 ismovable up and down vertically by the sealing jig elevating mechanism180 not shown in FIGS. 8A and 8B. The outside diameter of the sealingjig 181 which is perpendicular to its longitudinal direction is smallerthan the outside diameters of the washer 7, the ceramic supporters 8,and the powder compacts 9, and the inside diameter of the sealing jig181 is greater than the maximum sizes of the through holes of the washer7, the ceramic supporters 8, and the powder compacts 9. This structureallows the sealing jig 181 to depress the annular mounting parts fromthe vertical upper ends thereof.

In sealing, first, the sealing jig elevating mechanism 180 disposes thesealing jig 181 at a position vertically above the workpiece 40β held bythe inversion jig 171 at which the workpiece 40β is coaxial with thesealing jig 181. Subsequently, as indicated by the arrow AR9 in FIG. 8A,the sealing jig elevating mechanism 180 moves down the sealing jig 181.As the sealing jig 181 starts moving downward, the sealing jig 181eventually abuts the upper surface of the washer 7, which is positionedat the uppermost position among the annular mounting parts annularlymounted to the sensor element 10. As the sealing jig 181 is moved downfurther from this state, as shown in FIG. 8B, the washer 7 and furtherthe whole of the annular mounting parts are pressed vertically downwardinside the tubular body 30 whose outer periphery is held by theinversion jig 171. In this case, the position of the tubular body 30 isfixed through the fixing by the inversion jig 171, and consequently, thepowder compacts 9 (9 a, 9 b) are compressed to predetermined thicknessesbetween the washer 7 and the ceramic supporter 8 c. As a result, a spacebetween the first tip 10 a side of the sensor element 10, which includesthe gas inlet 11, and the second tip 10 b, which includes the terminals13 for connection with the cable C, is sealed. This achievesairtightness between the measurement gas space and the reference gasspace in the gas sensor 1. In this case, the sealing jig 181 and thesealing jig elevating mechanism 180 function as press means forcompressing the powder compact by pressing. If the sealing jig 181preferably functions as such press means, the tip thereof that abuts thewasher 7 does not need to be formed continuously in its radial directionand can be formed non-continuously, for example, can have a slit.

Although the sensor element 10 is also fixed inside the tubular body 30through the sealing with the compression of the powder compacts 9 in themanner above, until the sensor element 10 is fixed as described above,the sensor element 10 is displaceable vertically though it is partiallyin contact with the annular mounting parts and the housing 5. In theassembly apparatus 100 according to this embodiment, however, by causingthe first tip 10 a of the sensor element 10 (more specifically, theprotective film P) to come into contact with the sealing assist jig 111prior to sealing as described above, the sensor element 10 can beprevented from sliding out of place vertically downward from itsoriginally disposed position along with sealing, thus keeping theposition of the sensor element 10 within a predetermined tolerance.

Besides, the impact buffer 112 is provided at the vertical upper end ofthe sealing assist jig 111, so that the force by which the sensorelement 10 is pressed against the sealing assist jig 111 along with thepressing by the sealing jig 181 is absorbed by the impact buffer 112.This preferably prevents a situation in which an impact associated withpressing is exerted on the protective film P covering the first tip 10 aor further the first tip 10 a itself, and consequently, the protectivefilm P and the first tip 10 a are damaged.

The impact buffer 112 does not necessarily exhibit an operationaladvantage only when it is used to assemble the sensor element 10 withthe protective film P. The impact buffer 112 has an effect of preventingdamage to the first tip 10 a including the gas inlet 11 and the vicinityof the first tip 10 a in sealing even when the sensor element 10 withoutthe protective film P is to be assembled.

When the sealing jig 181 completes sealing, the crimp jig drivemechanism 190 crimps the inner tube 6. Specifically, with the sealingjig 181 performing pressing, the crimp jig drive mechanism 190 not shownin FIGS. 9A and 9B runs, thus causing, as indicated by the arrow AR10 inFIG. 9A, the crimp jig 191 to approach the inner tube 6 from the lateralside of the inner tube 6 and crimp the inner tube 6 from its outerperipheral side at the height level immediately above the washer 7.Since the compression of the powder compacts 9 by the sealing jig 181described above provides a space that is located inside the inner tube 6and is above the washer 7, as shown in FIG. 9B, such crimping preferablyforms the recess 6 b at the position immediately above the washer 7 inthe inner tube 6. The formation of the recess 6 b prevents the annularmounting parts from falling off in the following steps, and the annularmounting parts are locked inside the tubular body 30 as described above.In this case, the crimp jig 191 and the crimp jig drive mechanism 190function as crimp means for forming the recess 6 b that locks theannular mounting parts in the inner tube 6 constituting the tubular body30. Subsequent to the formation of the recess 6 b, retightening may beperformed in which the inner tube 6 is crimped at the posture lateral tothe powder compact 9 a. This more reliably locks the annular mountingparts inside the tubular body 30 and provides hermitical sealing in thegas sensor 1.

The formation of the recess 6 b (or retightening performed thereafter)described above completes the assembly 40. After the formation of therecess 6 b, the sealing jig elevating mechanism 180 not shown in FIGS.9A and 9B runs again, thus causing the sealing jig 181 to retract to apredetermined retraction position as indicated by the arrow AR11 in FIG.9B. Finally, the assembly transport mechanism 200 not shown in FIGS. 9Aand 9B transports the assembly 40 to the assembly wait part 201. Aspecific configuration of the assembly transport mechanism 200 may beany configuration that can preferably transport the assembly 40.

Consequently, the assembly procedure in the assembly apparatus 100completes. When another assembly 40 is assembled subsequently, a similarprocedure is repeated from the state shown in FIG. 5A. The resultantassembly 40 is taken out of the assembly apparatus 100 and is equippedwith the first cover 2, the fixing bolt 3, and the second cover 4. Thiscompletes (the main body of) the gas sensor 1.

The annular mounting parts are always annularly mounted to the elementdummy or the sensor element through the procedure for assembling anassembly performed in this embodiment. This state preferably prevents anoccurrence of a problem in which a sensor element cannot be incorporateddue to an occurrence of a positional deviation.

The first tip of the sensor element provided with an opening does notpass through the through holes of the annular mounting parts, and thus,even in the use of a sensor element including a protective film at thefirst tip side, assembling can be performed preferably.

Positioning of the sensor element by the sealing assist jig preferablyprevents a positional deviation occurring in the sensor element when theassembly is sealed.

The sealing assist jig, which includes the impact buffer, prevents theprotective film provided on the sensor element or the sensor elementitself from experiencing a strong impact in sealing, thereby sealing theassembly without damaging the protective film or the sensor element.

Modification of First Embodiment

The assembly apparatus 100 according to the first embodiment isconfigured as follows: the impact buffer 112 provided at the verticalupper end of the sealing assist jig 111 provides a buffer performanceagainst an impact exerted from vertically above to the sealing assistjig 111, and damage to the protective film P is prevented by performingsealing while causing the protective film P provided at the first tip 10a of the sensor element 10 to be in contact with the impact buffer 112.The configuration of the sealing assist jig 111, however, is not limitedto the above and may be any configuration that can mitigate an impactexerted on the protective film P in pressing by the sealing jig 181.

FIG. 10 schematically shows a sealing assist jig 111 having aconfiguration different from that of the first embodiment. The sealingassist jig 111 shown in FIG. 10 includes, in its vertical midwayportion, an impact buffer 113 formed of an elastic member that iselastic in the vertical direction. A preferable example of the impactbuffer 113 is formed of a spring member. Also when this sealing assistjig 111 is provided, as in the embodiment described above, the workpiece40β is inverted by the inversion mechanism 170, and further, is disposedsuch that the first tip 10 a of the sensor element 10 covered with theprotective film P comes into contact with the vertical upper end of thesealing assist jig 111.

The sealing assist jig 111 is provided with the impact buffer 113 thoughits vertical upper end is merely a horizontal surface, and thus, also inthe configuration shown in FIG. 10, the force by which the sensorelement 10 is pressed against the sealing assist jig 111 is absorbed bythe impact buffer 113 in pressing by the sealing jig 181. Thispreferably prevents a situation in which an impact associated withpressing is exerted on the protective film P covering the first tip 10a, and consequently, the protective film P and the first tip 10 a aredamaged.

Similarly to the impact buffer 112, the impact buffer 113 does notnecessarily exhibit an operational advantage only when it is used toassemble the sensor element 10 provided with the protective film P. Inother words, the impact buffer 113 has an effect of preventing damage tothe first tip 10 a provided with the gas inlet 11 and the vicinity ofthe first tip 10 a even when the sensor element 10 not provided with theprotective film P is to be assembled.

Second Embodiment

In the first embodiment and the modification thereof described above,the workpiece 40β is inverted vertically, and then, in sealing theinside of the tubular body 30, the jig that has a buffer performanceagainst an impact exerted from vertically above is used as the sealingassist jig 111 supporting the sensor element 10 from below. This enablessealing without damage to the protective film P and the first tip 10 aeven when the first tip 10 a of the sensor element 10 is provided withthe protective film P. The manner of sealing the inside of the tubularbody 30, however, is not limited to this. In this embodiment, sealing isperformed separately in two stages during assembly of the assembly 40.This will now be described in detail.

FIG. 11 is a block diagram showing a schematic configuration of anassembly apparatus 1100 that assembles an assembly 40 in thisembodiment. Some of the components of the assembly apparatus 1100 arecommon with the components of the assembly apparatus 100 according tothe first embodiment. These components are denoted by references similarto those of the assembly apparatus 100, and detailed description thereofwill be omitted.

Specifically, the assembly apparatus 1100 includes, as componentssimilar to those of the assembly apparatus 100, the control part 101mainly composed of the CPU 101 a, the ROM 101 b, and the RAM 101 c, theoperation part 102, the display part 103, the storage part 104 storingthe operation program 104 p and the like, the dummy elevating mechanism120, the element dummy 121, the annular mounting parts transportmechanism 130, the annular mounting parts wait part 131, the housingfixing jig drive mechanism 140, the housing fixing jig 141 including thesupport part 141 a and the movable part 141 b, the element transportmechanism 150, the element wait part 151, the element guide jig drivemechanism 160, the element guide jig 161, the crimp jig drive mechanism190, and the crimp jig 191.

The assembly apparatus 1100 further includes, as components thatactually perform assembly operations, an inversion mechanism 1170performing an operation of inverting the workpiece 40β with the firstinversion jig 1171 and the second inversion jig 1172, a temporarysealing jig elevating mechanism 1180A performing an operation of movingup and down a temporary sealing jig (depressing jig) 1181, a finalsealing jig elevating mechanism 1180B performing an operation of movingup and down a final sealing jig (abutment jig) 1182, a positioning jigelevating mechanism 1190 performing an operation of moving up and downan element positioning jig 1191, an assembly transport mechanism 1200transporting the workpiece 40β and the assembly 40, and an assembly waitpart 1201 storing the assembled assembly 40.

FIGS. 12A, 12B, 13, 14A, 14B, 15A, and 15B are schematic cross-sectionalviews of the assembly 40 during assembly for explaining the procedurefor assembling the assembly 40 by the assembly apparatus 1100. Also inFIGS. 12A to 15B, the vertically upward direction is represented by thez-axis direction as in FIGS. 5A to 9B.

Of the procedure for assembling the assembly 40 by the assemblyapparatus 1100, annularly mounting of the annular mounting parts to theelement dummy 121, annularly mounting of the tubular body 30 to theouter peripheries of the annular mounting parts, and changing of theelement dummy 121 and the sensor element 10 are performed as in thefirst embodiment, that is, as in the manner shown in FIGS. 5A to 6C.Description thereof will thus be omitted in this embodiment.

After changing of the sensor element 10 and the element dummy 121completes, the workpiece 40β is transported by the assembly transportmechanism 1200 while keeping its posture and, as shown in FIG. 12A, isplaced on the sealing assist jig (support jig) 1192.

The sealing assist jig 1192 is a cylindrical member, included in theassembly apparatus 1100, with a flat upper end and its longitudinaldirection coinciding the z-axis direction, and is configured to supportthe workpiece 40β from below by its upper end abutting the washer 7. Theoutside diameter of the upper end of the sealing assist jig 1192 issmaller than the inside diameter of the tubular body 30 (and the outerdiameter of each annular mounting part). The inside diameter of theupper end of the sealing assist jig 1192 is greater than a maximum sizeof the through hole of each annular mounting part.

The second tip 10 b of the sensor element 10 projecting verticallydownward is inserted into the through hole 1192 a of the sealing assistjig 1192 in the placing of the workpiece 40β (supporting the workpiece40β from below). For this reason, the sealing assist jig 1192 does notinterfere with the sensor element 10. Here, the element positioning jig1191 is provided in the through hole 1192 a.

The element positioning jig 1191 serves to determine the position atwhich the sensor element 10 is disposed vertically (to posture thesensor element 10) in temporary sealing described below. The elementpositioning jig 1191 is movable up and down vertically by thepositioning jig elevating mechanism 1190 and is disposed such that itsupper end is disposed at the position at which the lower end of thesensor element 10 is disposed after temporary sealing.

Although the lower end of the sensor element 10 abuts the upper end ofthe element positioning jig 1191 in FIG. 12A, this abutment is notnecessarily required at the time when the workpiece 40β is placed on thesealing assist jig 1192.

When the workpiece 40β is placed on the sealing assist jig 1192 and thesensor element 10 is positioned as described above, temporary sealing(primary compression) is performed, which is the first sealing of theinside of the workpiece 40β, by the compression of the powder compacts 9(9 a, 9 b) using the temporary sealing jig 1181. Temporary sealing is asealing step whose main objective is to temporarily fix the sensorelement 10 inside the workpiece 40β. The reason why “temporary” ismentioned here is that the sensor element 10 displaces slightly from afirst position in the final sealing (secondary compression) performedthereafter.

The temporary sealing jig 1181 is a cylindrical member with itslongitudinal direction coinciding the vertical direction. The temporarysealing jig 1181 is movable up and down vertically by the temporarysealing jig elevating mechanism 1180A not shown in FIGS. 12A and 12B.More specifically, when the temporary sealing jig 1181 is movedvertically downward as indicated by the arrow AR14 while the workpiece40β is supported from below by the sealing assist jig 1192, the lowerend of the temporary sealing jig 1181 abuts a projection portion(flanged portion) 5 b provided on the outer periphery of the housing 5constituting the tubular body 30. In other words, at least the lower endof the temporary sealing jig 1181 and the vicinity thereof have adiameter and a thickness enough to perform such abutment.

The temporary sealing jig 1181 has a cavity 1181 a therein that is openupward. With the workpiece 40β placed on the sealing assist jig 1192,the first tip 10 a of the sensor element 10 provided with the protectivefilm P projects vertically upward from the end of the tubular body 30.When the temporary sealing jig 1181 abuts the projection portion 5 b,however, the first tip 10 a is inserted into the cavity 1181 a of thetemporary sealing jig 1181, so that the sealing assist jig 1192 does notinterfere with the sensor element 10. This prevents the protective filmP from being damaged or peeled off to be broken.

The temporary sealing jig 1181 is moved down further even after thelower end thereof abuts the projection portion 5 b of the housing 5.Then, the tubular body 30 is pressed vertically downward along with thetemporary sealing jig 1181 being moved downward, as indicated by thearrow AR15. The annular mounting parts inside the tubular body 30 aresupported from below by the sealing assist jig 1192, and thus, begin tokeep their positions. Along with the tubular body 30 moving downward,accordingly, the washer 7 is pushed into a relatively inner portion ofthe tubular body 30. Consequently, the upper end of the sealing assistjig 1192 presses the washer 7, resulting in a state in which avertically upward force (load) F1 (first force) is applied to the washer7. If the force F1 is preferably applied to the washer 7, both of thetip of the sealing assist jig 1192 that abuts the washer 7 and the tipof the temporary sealing jig 1181 that abuts the projection portion 5 bof the housing 5 do not need to be formed continuously in the radialdirection and can be formed non-continuously, for example, can have aslit.

When the force F1 is exerted on the washer 7 from the sealing assist jig1192, the force F1 is also exerted as a compression force on the powdercompacts 9 a and 9 b through the ceramic supporters 8 a and 8 b. Thepowder compacts 9 a and 9 b are accordingly compressed, and the annularmounting parts are pushed into the tubular body 30 as a whole. Suchcompression eliminates the gap between the powder compacts 9 a and 9 band the sensor element 10, thus bringing the powder compacts 9 a and 9 binto intimate contact with the sensor element 10. The sensor element 10,which has been displaceable vertically, is fixed by the powder compacts9 a and 9 b while being positioned by the element positioning jig 1191.This is the temporary sealing performed in this embodiment. The disposedposition of the sensor element 10 in the workpiece 400 after thetemporary sealing disposed is referred to as a first position.

Here, the force F1 is applied with magnitude in such a range that doesnot cause chipping (or cracking) in the sensor element 10 while enablingfixing of the sensor element 10. In other words, in the temporarysealing, the powder compacts 9 are not compressed to such an extent thatachieves sufficient airtightness though it is compressed to such anextent that allows the sensor element 10 to be fixed. The airtightnessis achieved in a following final sealing step.

In the case where the first position at which the sensor element 10 ispositioned is lowered beyond an allowable lower limit position duringthe temporary sealing, the positioning jig elevating mechanism 1190 ismoved up to prevent the first position from being located below thelower limit position.

As shown in FIG. 12B, the assembly apparatus 1100 may include a laserdisplacement meter 1185 to monitor the height level of the sensorelement 10 by emitting a laser beam LB toward the first tip 10 a of thesensor element 10 exposed in the cavity 1181 a from the laserdisplacement meter 1185. In this case, the positioning jig elevatingmechanism 1190 and the element positioning jig 1191 can posture thesensor element 10 based on the monitoring result.

After the temporary sealing completes, the temporary sealing jig 1181 iscaused to retract, and with the posture of the workpiece 40β kept by theassembly transport mechanism 1200, the workpiece 40β is delivered to thefirst inversion jig 1171 and the second inversion jig 1172.

The inversion mechanism 1170 vertically inverts the posture of theworkpiece 40β after being temporary sealed which has been delivered fromthe assembly transport mechanism 1200. Specifically, first, theinversion mechanism 1170 drives the first inversion jig 1171 and thesecond inversion jig 1172 to cause, as shown in FIG. 13, each of thefirst inversion jig 1171 and the second inversion jig 1172 of theinversion mechanism 1170 to grip the workpiece 40β. The first inversionjig 1171 grips the sensor element 10 projecting vertically downward inthe lower part of the workpiece 40β from the lateral side of the sensorelement 10, and the second inversion jig 1172 grips the tubular body 30(more specifically, the housing 5) from the lateral side of the tubularbody 30.

The inversion mechanism 1170 then moves the first inversion jig 1171 andthe second inversion jig 1172 to cause these jigs to orbit around apredetermined horizontal axis by 180° while keeping the grip states ofthese jigs such that the portion gripped by the first inversion jig 1171and the portion gripped by the second inversion jig 1172 are verticallyinverted. This vertically inverts the posture of the workpiece 40β asindicated by the arrow AR16. In other words, the workpiece 40β ispostured such that the first tip 10 a side of the sensor element 10provided with the protective film P is the lowermost end. In this case,the first inversion jig 1171, the second inversion jig 1172, and theinversion mechanism 1170 function as inversion means for verticallyinverting the posture of the workpiece 40β. Specific configurations ofthe first inversion jig 1171, the second inversion jig 1172, and theinversion mechanism 170 may be any configurations that preferably enablethe inversion of the posture of the workpiece 40β.

In this embodiment, the powder compacts 9 are compressed to some extentby the temporary sealing prior to the inversion of the posture, so thatthe powder compacts 9 are less likely to fall off (drop) due to theinversion than in the first embodiment in which the workpiece 40β isinverted without temporary sealing.

As shown in FIG. 14A, the workpiece 40β whose posture has been invertedis placed on a transport palette 1210 included in the assembly transportmechanism 1200. In the assembly transport mechanism 1200, the transportpalette 1210 is movable up and down vertically. The transport palette1210 is also used to transport, to the assembly wait part 1201, theassembly 40 obtained after all the assembling steps complete.

The transport palette 1210 includes, at the side of its upper surfaceperpendicular to the vertical direction, a fitting part 1210 a that is arecess having a shape corresponding to the housing 5 constituting theassembly 40. Fitting the housing 5 with the fitting part 1210 a causesthe workpiece 40β to be placed on and fixed to the transport palette1210 in such a posture that causes its longitudinal direction to extendvertically.

Preferably, when being placed and fixed, the workpiece 40β is positionedso as not to have a rotational deviation in the horizontal plane. Thismay be achieved by providing anisotropy to the outer peripheral shape ofthe housing 5 and providing the fitting part 1210 a with a shapecorresponding to the outer peripheral shape. Alternatively, retainingmeans (not shown) included in the transport palette 1210 may retain thehorizontal posture of the workpiece 40β.

Below the fitting part 1210 a, a hole portion 1210 b is provided.Although the first tip 10 a of the sensor element 10 provided with theprotective film P projects vertically downward from the end of thetubular body 30 in the lower part of the workpiece 40β, when theworkpiece 40β is placed on the transport palette 1210, the first tip 10a is inserted into the hole portion 1210 b, and thus, does not interferewith the transport palette 1210. This prevents the protective film Pfrom being damaged or peeled off to be broken.

When the workpiece 40β is placed on and fixed to the transport palette1210, subsequently, final sealing (secondary compression) is performed.The final sealing is a sealing step performed to mainly achieveairtightness between the measurement gas space and the reference gasspace.

In the final sealing, a final sealing jig elevating mechanism 1180B notshown in FIG. 14A causes the final sealing jig 1182 to move verticallydownward from above the workpiece 40β as indicated by the arrow AR17 inFIG. 14A, to cause the lower end of the final sealing jig 1182 to abutthe washer 7.

The final sealing jig 1182 is a cylindrical member with its longitudinaldirection coinciding the vertical direction, and is movable up and downvertically by the final sealing jig elevating mechanism 1180B. Theoutside diameter of the final sealing jig 1182 perpendicular to itslongitudinal direction is smaller than the outside diameter of eachannular mounting part, and the inside diameter of the final sealing jig1182 is greater than a maximum size of the through hole of each annularmounting part.

The final sealing jig 1182 abuts the washer 7, causing the assemblytransport mechanism 200 to move up the transport palette 1210 verticallyas indicated by the arrow AR18 in FIG. 14B.

Then, along with the transport palette 1210 moving upward, the tubularbody 30 is pushed vertically upward. On the other hand, the finalsealing jig 1182 abuts the washer 7 that is located uppermost among theannular mounting parts inside the tubular body 30, and thus, the annularmounting parts begin to keep their positions. The washer 7 isaccordingly pushed into a relatively inner portion of the tubular body30 along with the transport palette 1210 moving upward. Consequently,the lower end of the final sealing jig 1182 presses the washer 7,resulting in a state in which a vertically downward force (load) F2(second force) is applied to the washer 7. If the force F2 is preferablyapplied to the washer 7, the tip of the final sealing jig 1182 thatabuts the washer 7 does not need to be formed continuously in the radialdirection and can be formed non-continuously, for example, can have aslit.

When the force F2 is exerted on the washer 7 from the final sealing jig1182, the force F2 is also exerted as a compression force on the powdercompacts 9 a and 9 b through the ceramic supporters 8 a and 8 b. In thiscase, if F2>F1, the powder compacts 9 a and 9 b are compressed further,and the annular mounting parts are further pushed into the tubular body30 as a whole. Consequently, the space between the measurement gas spaceand the reference gas space is hermetically sealed. This is the finalsealing performed in this embodiment.

During the final sealing, the first tip 10 a of the sensor element 10provided with the protective film P is inserted into the hole portion1210 b and does not abut another member. This prevents the protectivefilm P from being damaged or peeled off to be broken during the finalsealing.

In the first embodiment, when the assembly 40 is sealed, the protectivefilm P is protected from breakage with the use of the sealing assist jig111 that has a buffer performance against an impact; according to thisembodiment, the first tip 10 a of the sensor element 10 provided withthe protective film P does not abut another member in the temporarysealing and the final sealing, so that without the use of the sealingassist jig 111, sealing can be achieved in the assembly 40 whileprotecting the protective film P from breakage.

For reliable hermetic sealing, the force F2 applied to the washer 7needs to be much greater than the force F1 applied to the washer 7 inthe temporary sealing. On the other hand, the final sealing is performedwithout causing the sensor element 10 to abut another member not only atthe first tip 10 a side but also at the second tip 10 b side. The sensorelement 10, which has been fixed by the powder compacts 9 a and 9 b oncein the temporary sealing stage and has been disposed at the firstposition, thus can be displaced further by even a small amount in thefinal sealing. On the premise that the disposed position of the sensorelement 10 after the final sealing is referred to as a second position,however, if the second position falls within a predetermined error rangeallowable in terms of characteristics desired for the gas sensor 1, thesensor element 10 can be regarded as being preferably fixed at thesecond position even upon occurrence of such a displacement.

In the final sealing, thus, the transport palette 1210 is moved up suchthat the pressure to be applied to the washer 7 by the final sealing jig1182 has magnitude that causes the second position to fall within apredetermined allowable error range. The upper limit of the pressure canbe appropriately determined in view of, for example, material strengthsof the final sealing jig 1182 and the washer 7, or the ceramicsupporters 8.

Two-stage sealing performed in this embodiment has an effect that a riskof chipping or cracking occurring in the sensor element 10 is reducedcompared with the manner of performing sealing only once.

Specifically, in hermitic sealing, a strong force needs to be applied tocompress the powder compacts 9, whereas the sensor element 10 needs tobe positioned at a predetermined position. Hermitic sealing with thesensor element 10 abutting another member for positioning exerts astrong force also on the portion at which the sensor element 10 abutsthe other member, which may cause chipping or cracking occurring in thesensor element 10.

In this embodiment, contrastingly, in the temporary sealing forpositioning the sensor element 10, the compression force exerted on thepowder compacts 9 is set to be smaller than the force required forhermitic sealing, though the sensor element 10 is caused to abut theelement positioning jig 1191. In the final sealing thereafter, thecompression force applied to the powder compacts 9 is set large enoughto enable hermitic sealing, whereas the sensor element 10 that has beenpositioned to some extent is prevented from abutting another member.This prevents a strong force to be exerted on the portion at which thesensor element 10 abuts the other member, leading to a lower risk ofchipping or cracking occurring in the sensor element 10.

When the final sealing completes, the crimp jig drive mechanism 190crimps the inner tube 6 as in the first embodiment. Specifically, withthe transport palette 1210 and the final sealing jig 1182 remainingdisposed also after the final sealing, the crimp jig drive mechanism 190not shown in FIGS. 15A and 15B runs, thus causing, as indicated by thearrow AR19 in FIG. 15A, the crimp jig 191 to approach the inner tube 6from the lateral side of the inner tube 6 and crimp the inner tube 6from its outer peripheral side at the height level immediately above thewasher 7. As a result of the final sealing described above, a space isformed inside the inner tube 6 above the washer 7, and thus, the recess6 b is preferably formed at a position immediately above the washer 7 inthe inner tube 6, as shown in FIG. 15B. The formation of the recess 6 bprevents the annular mounting parts from falling off in the followingsteps, and as described above, the annular mounting parts are lockedinside the tubular body 30. In this case, the crimp jig 191 and thecrimp jig drive mechanism 190 function as crimp means for forming therecess 6 b that locks the annular mounting parts in the inner tube 6constituting the tubular body 30. Also in this embodiment, retighteningmay be performed following the formation of the recess 6 b as in thefirst embodiment.

The formation of the recess 6 b described above (or retighteningthereafter) completes the assembly 40. After the formation of the recess6 b, the final sealing jig elevating mechanism 1180B not shown in FIGS.15A and 15B runs again, thus causing the final sealing jig 1182 to moveupward as indicated by the arrow AR20 in FIG. 15B and retract to apredetermined retraction position. Also, the assembly transportmechanism 1200 not shown in FIGS. 15A and 15B causes the transportpalette 1210 to move vertically downward as indicated by the arrow AR21in FIG. 15B and return to the position before the final sealing. Afterthat, the assembly transport mechanism 1200 transports the assembly 40to the assembly wait part 1201.

Consequently, the assembly procedure in the assembly apparatus 1100completes. When another assembly 40 is subsequently assembled, a similarprocedure is repeated from the state shown in FIG. 5A. The resultantassembly 40 is provided to the outside of the assembly apparatus 1100and is then equipped with the first cover 2, the fixing bolt 3, and thesecond cover 4. This completes (the main body) of the gas sensor 1.

Also in the procedure for assembling an assembly performed in thisembodiment, as in the first embodiment, the annular mounting parts arealways annularly mounted to the element dummy or the sensor element.This preferably prevents a problem in which the sensor element cannot beassembled due to the occurrence of a positional deviation.

The first tip of the sensor element having an opening does not passthrough the through holes of the annular mounting parts, and thus, evenin the use of a sensor element including a protective film at its firsttip side, assembling can be performed preferably.

In this embodiment, the first tip of the sensor element provided withthe protective film does not abut another member in the temporarysealing and the final sealing. Without the use of a sealing assist jigas used in the first embodiment, thus, sealing can be performed in theassembly while protecting the protective film from breakage.

A strong force is not exerted on the portion at which the sensor elementabuts another member in both of the temporary sealing and the finalsealing, leading to a lower risk of chipping or cracking occurring inthe sensor element than in the case where sealing is performed while thesensor element abuts another member.

As in the assembly procedure described in the first embodiment, theassembly procedure in this embodiment does not necessarily exhibit anoperational advantage only when it is used to assemble a sensor elementprovided with a protective film. That is to say, the assembly procedurein this embodiment can similarly achieve an operational effectirrelevant to a protective film also when a sensor element not providedwith a protective film is to be assembled.

Modification of Second Embodiment

In the second embodiment described above, the final sealing is performedby moving up the transport palette 1210, with the final sealing jig 1182abutting the washer 7. Alternatively, the final sealing may be performedby moving down the final sealing jig 1182 abutting the washer 7vertically downward, with the transport palette 1210 remainingstationary.

1. A method for assembling a gas sensor, the method comprising the stepsof: (a) disposing an element dummy with its longitudinal directioncoinciding a vertical direction, said element dummy having a shapesimilar to a shape of a sensor element including ceramic as a mainconstituent material and having an elongated shape; (b) fitting throughholes of annular mounting parts with said element dummy from verticallyabove, said annular mounting parts each having a disc shape orcylindrical shape, said through holes each having a shape correspondingto a cross-sectional shape of said sensor element; (c) fitting a tubularbody with outer peripheries of said annular mounting parts fromvertically above; (d) abuttingly disposing said sensor element on anupper end of said element dummy such that said element dummy and saidsensor element are arranged in line with each other; (e) moving saidelement dummy vertically downward to move down said sensor element andfitting said through holes of said annular mounting parts with saidsensor element, to thereby obtain a workpiece including said sensorelement, said annular mounting parts, and said tubular body; (f)vertically inverting a posture of said workpiece; and (g) pressing saidannular mounting parts, wherein in said step (a), a plurality of typesof parts including a powder compact of ceramic are fitted with saidelement dummy as said annular mounting parts, and said step (g) includesa step of compressing said powder compact and is performed at leastafter said step (f).
 2. The method according to claim 1, wherein in saidstep (g), with a tip of said sensor element, located as a lowermost endof said workpiece after said step (f), being in contact with a sealingassist jig, said part located at an uppermost position among saidannular mounting parts is pressed vertically downward to compress saidpowder compact, to thereby seal an inside of said tubular body, saidsealing assist jig having a buffer performance against an impact exertedfrom vertically above.
 3. The method according to claim 2, wherein saidsensor element has a surface of one end on which a protective film isformed, in said step (d), said sensor element is disposed such that anend of said sensor element at a side at which said protective film isnot formed is supported by said element dummy, and in said step (g),with said protective film being in contact with said sealing assist jig,said part located at said uppermost position is pressed verticallydownward.
 4. The method according to claim 2, wherein said sealingassist jig includes a buffer member having a buffer performance againstan impact exerted from vertically above.
 5. The method according toclaim 4, wherein said buffer member has a Rockwell hardness of 1 or moreand 200 or less and a thickness of 0.1 mm or more and 1.0 mm or less. 6.The method according to claim 2, wherein said sealing assist jigincludes, in its vertical midway portion, an elastic member having abuffer performance against an impact exerted from vertically above. 7.The method according to claim 1, wherein said step (g) includes (g-1) astep of compressing said powder compact of said workpiece being in afirst posture, and (g-2) a step of compressing said powder compact ofsaid workpiece being in a second posture, said first posture being aposture of said workpiece before being vertically inverted in said step(f), said second posture being a posture of said workpiece after beingvertically inverted in said step (f), and letting an upper end and alower end of said sensor element when said workpiece is in said firstposture be respectively a first tip and a second tip, in said step(g-1), with said sensor element being positioned from below said secondtip using a predetermined positioning jig, a first force is applied tosaid annular mounting parts vertically upward to compress said powdercompact, in said step (f), said workpiece in which said powder compacthas been compressed in said step (g-1) is vertically inverted, and insaid step (g-2), with said workpiece vertically inverted in said step(f) being supported from below and simultaneously said first tip of saidsensor element located at a lowermost end of said workpiece beingprevented from abutting another member, a second force greater than saidfirst force is applied to said annular mounting parts verticallydownward to further compress said powder compact, to thereby seal aninside of said tubular body.
 8. The method according to claim 7, whereinsaid sensor element has a surface of one end on which a protective filmis formed, and in said step (d), said sensor element is disposed suchthat an end of said sensor element at a side at which said protectivefilm is not formed is supported by said element dummy.
 9. The methodaccording to claim 7, wherein in said step (g-1), with said sensorelement being positioned from below using the positioning jig andsimultaneously said annular mounting parts being supported from belowusing a predetermined support jig, said workpiece is depressed fromabove using a predetermined depressing jig to cause said predeterminedsupport jig to press said part located at a lowermost position amongsaid mounting parts vertically upward, to thereby apply said first forceto said annular mounting parts vertically upward.
 10. The methodaccording to claim 7, wherein in said step (g-2), said part located atan uppermost position among said annular mounting parts is pressedvertically downward to apply said second force to said annular mountingparts vertically downward.
 11. The method according to claim 10, whereinin said step (g-2), with a predetermined abutment member being caused toabut said part located at the uppermost position among said annularmounting parts from vertically above, said workpiece is moved verticallyupward to apply said second force to said annular mounting partsvertically downward.
 12. The method according to claim 1, furthercomprising the step of (h) after said step (g), crimping an upper end ofsaid tubular body at a position immediately above said part located atan uppermost position among said annular mounting parts from an outerperipheral side of said tubular body to form a recess that locks saidannular mounting parts.
 13. The method according to claim 12, wherein insaid step (h), a cavity formed immediately above said part located atthe uppermost position inside said tubular body in said pressing step iscrimped.
 14. A gas sensor assembly apparatus, comprising: an elementdummy having a shape similar to a shape of a sensor element includingceramic as a main constituent material and having an elongated shape; adummy disposing element that disposes said element dummy with itslongitudinal direction coinciding a vertical direction; an annularmounting parts fitting element that fits through holes of annularmounting parts with said element dummy from vertically above, saidannular mounting parts each having a disc shape or cylindrical shape,said through holes each having a shape corresponding to across-sectional shape of said sensor element; a tubular body fittingelement that fits a tubular body with outer peripheries of said annularmounting parts from vertically above; an element disposing element thatabuttingly disposes said sensor element on an upper end of said elementdummy such that said element dummy and said sensor element are arrangedin line with each other; an element fitting element that moves down saidelement dummy vertically downward to move down said sensor element andfits said through holes of said annular mounting parts with said sensorelement, to thereby obtain a workpiece including said sensor element,said annular mounting parts, and said tubular body; an inversion elementthat vertically inverts a posture of said workpiece; and a pressingelement that presses said annular mounting parts, wherein said annularmounting parts comprise a plurality of types of parts including a powdercompact of ceramic, and said pressing element presses said annularmounting parts at least after said inversion element vertically invertsthe posture of said workpiece to compress said powder compact.
 15. Thegas sensor assembly apparatus according to claim 14, further comprising:a sealing assist jig having a buffer performance against an impactexerted from vertically above, wherein said inversion element causes atip of said sensor element that is located as a lowermost end of saidworkpiece after the posture is vertically inverted to come into contactwith said sealing assist jig, and with said tip of said sensor elementbeing in contact with said sealing assist jig, said pressing elementpresses said part located at an uppermost position among said annularmounting parts vertically below to compress said powder compact, tothereby seal an inside of said tubular body.
 16. The gas sensor assemblyapparatus according to claim 15, wherein said sensor element has asurface of one end on which a protective film is formed, said elementdisposing element disposes said sensor element such that an end of saidsensor element at a side at which said protective film is not formed issupported by said element dummy, and with said protective film being incontact with said sealing assist jig, said pressing element presses saidpart located at said uppermost position vertically downward.
 17. The gassensor assembly apparatus according to claim 15, wherein said sealingassist jig includes, at its vertical upper end, a buffer member having abuffer performance against an impact exerted from vertically above. 18.The gas sensor assembly apparatus according to claim 17, wherein saidbuffer member has a Rockwell hardness of 1 or more and 200 or less and athickness of 0.1 mm or more and 1.0 mm or less.
 19. The gas sensorassembly apparatus according to claim 15, wherein said sealing assistjig includes, in its vertical midway portion, an elastic member having abuffer performance against an impact exerted from vertically above. 20.The gas sensor assembly apparatus according to claim 14, wherein saidpressing element includes a primary compression element that compressessaid powder compact of said workpiece being in a first posture, and asecondary compression element that compresses said powder compact ofsaid workpiece being in a second posture, said first posture being aposture of said workpiece that is not vertically inverted by saidinversion element, said second posture being a posture of said workpiecethat is vertically inverted by said inversion element, and letting anupper end and a lower end of said sensor element when said workpiece isin said first posture be respectively a first tip and a second tip, saidprimary compression element includes a positioning jig that positionssaid sensor element from below said second tip, said primary compressionelement applying a first force to said annular mounting parts verticallyupward to compress said powder compact, with said sensor element beingpositioned by said positioning jig, said inversion element verticallyinverts said workpiece in which said powder compact is compressed bysaid primary compression element, and while supporting, from below, saidworkpiece vertically inverted by said inversion element andsimultaneously preventing said first tip of said sensor element locatedat a lowermost end of said workpiece from abutting another member, saidsecondary compression element applies a second force greater than saidfirst force to said annular mounting parts to further compress saidpowder compact, to thereby seal an inside of said tubular body.
 21. Thegas sensor assembly apparatus according to claim 20, wherein said sensorelement has a surface of one end on which a protective film is formed,and said element disposing element disposes said sensor element suchthat an end of said sensor element at a side at which said protectivefilm is not formed is supported by said element dummy.
 22. The gassensor assembly apparatus according to claim 20, wherein said primarycompression element further includes a support jig that supports saidannular mounting parts from below, and a depressing jig that depressessaid workpiece from above, and while positioning said sensor elementfrom below using said positioning jig and simultaneously supporting saidannular mounting parts from below using said support jig, said primarycompression element depresses said workpiece from above using saiddepressing jig to press said part located at a lowermost position amongsaid annular mounting parts vertically upward using said support jig, tothereby apply said first force to said annular mounting parts verticallyupward.
 23. The gas sensor assembly apparatus according to claim 20,wherein said secondary compression element presses said part located atan uppermost position among said annular mounting parts verticallydownward to apply said second force to said annular mounting partsvertically downward.
 24. The gas sensor assembly apparatus according toclaim 23, wherein said secondary compression element further includes anabutment member that is caused to abut said part located at theuppermost position among said annular mounting parts from verticallyabove, and while causing said abutment member to abut said part, saidsecondary compression element moves said workpiece vertically upward toapply said second force to said annular mounting parts verticallydownward.
 25. The gas sensor assembly apparatus according to claim 14,further comprising a crimp element that crimps an upper end of saidtubular body at a position immediately above said part located at anuppermost position among said annular mounting parts from an outerperiphery of said tubular body to form a recess that locks said annularmounting parts.
 26. The gas sensor assembly apparatus according to claim25, wherein said crimp element crimps a cavity formed immediately abovesaid part located at the uppermost position inside said tubular body bysaid press element.
 27. The method according to claim 3, wherein saidsealing assist jig includes, at its vertical upper end, a buffer memberhaving a buffer performance against an impact exerted from verticallyabove.
 28. The method according to claim 3, wherein said sealing assistjig includes, in its vertical midway portion, an elastic member having abuffer performance against an impact exerted from vertically above. 29.The gas sensor assembly apparatus according to claim 16, wherein saidsealing assist jig includes, in its vertical upper end, a buffer memberhaving a buffer performance against an impact exerted from verticallyabove.
 30. The gas sensor assembly apparatus according to claim 16,wherein said sealing assist jig includes, in its vertical midwayportion, an elastic member having a buffer performance against an impactexerted from vertically above.